This invention generally pertains to the fields of cell biology and medicine. In particular, this invention provides novel libraries of nucleic acids encoding odorant/ligand-binding domains. Also provided are libraries of hybrid 7-transmembrane olfactory receptors comprising these odorant ligand-binding domains. The compositions and methods of the invention can be used to identify novel ligand-binding domains for olfactory neuron odorant receptors and their ligands. Thus, the compositions and methods of the invention can be used to generate novel odorants and to manipulate an animal""s olfactory response.
A better understanding of the vertebrate olfactory system would provide improved means to manipulate this process and possibly prevent disease or injury. For example, means to manipulate human olfactory neuron odorant receptors from healthy individuals and from individuals with neuro-psychiatric illnesses would offer systems for testing possible odorant/ligands for therapeutic and toxic effects. However, our ability to detect and discriminate between the thousands of beneficial or toxic odorants is complicated by the fact that odorant receptors belong to a multigene family with at least 500 to 1000 members. Furthermore, each olfactory receptor neuron may express only one, or at most a few, of these olfactory receptors. Any given olfactory neuron cell can respond to a small, arbitrary set of odorant-ligands. Odorant discrimination for a given neuron may depend on the ligand specificity of the one or few receptors it expresses. Thus, given this systems"" complexity, information about odorant/ligand-receptor recognition remains meager.
To analyze odorant/ligand-receptor interactions and their effects on cell physiology, it is first necessary to identify specific odorant/ligand(s) and the olfactory receptors to which they specifically bind. Such analysis requires isolation and expression of olfactory receptor polypeptides. However, despite the fact that many putative olfactory receptors have been cloned, only limited progress has been made in the functional expression of these receptors because present systems fail to efficiently translocate these 7-transmembrane proteins to the plasma membrane. This may be because olfactory receptors are a subclass of 7-transmembrane-domain receptors. For example, expression of one rat olfactory receptor in insect cells resulted in only a modest elevation in second messengers when exposed to a mixture of odorants; responses to single compounds were not seen (Raming (1993) Nature 361:353-356). The present invention addresses these and other needs.
The present invention provides novel compositions and methods to generate great numbers, or libraries, of odorant receptor ligand-binding regions. Also provided are novel chimeric olfactory receptors that incorporate these libraries of odorant binding domains. The present invention also provides novel compositions and methods to efficiently translocate polypeptides to the plasma membrane surface. Another aspect of the invention is based on the surprising discovery of a peptide domain that, when incorporated into a polypeptide, can with great efficiency xe2x80x9cchaperonexe2x80x9d or translocate the hybrid protein to the cell plasma membrane. Combining these two aspects of the invention also provides expression vectors and cells that efficiently express these recombinant proteins. Cells and transgenic animals efficiently expressing libraries of hybrid olfactory receptors can be used for screening potential beneficial and toxic odorant molecules.
The invention provides an amplification primer sequence pair for amplifying a nucleic acid encoding an olfactory receptor ligand-binding region comprising a first primer comprising a sequence 5xe2x80x2-GGGGTCCGGAG(A/G)(C/G)(A/G)TA(A/G/T)AT(A/G/P)A(A/G/P)(A/G/P)GG-3xe2x80x2 (SEQ ID NO:1) and a second primer comprising a sequence 5xe2x80x2-GGGGCTGCAGACACC(A/C/G/T)ATGTA(C/T)(C/T)T(A/C/G/T)TT(C/T)(C/T)T-3xe2x80x2 (SEQ ID NO:2). When used to amplify olfactory receptor nucleic acid sequences, it typically amplifies the receptor ligand-binding region comprising olfactory receptor transmembrane (TM) domains II through VII.
The invention also provides a method for generating nucleic acid sequence that encodes a ligand-binding region of an olfactory receptor, the method comprising amplification of a nucleic acid using the primer pair SEQ ID NO:1 and SEQ ID NO:2. In this method the amplified nucleic acid can be genomic DNA, mRNA or cDNA derived from olfactory neurons or olfactory epithelium. The amplification can be by polymerase chain reaction (PCR), wherein the PCR amplification comprises the following conditions and steps in the following order: about one cycle at about 94xc2x0 C. for about 2 min; and about 30 cycles of about 45xc2x0 C. to about 65xc2x0 C. for about 1 min, followed by about 72xc2x0 C. for about one min. followed by about 94xc2x0 C. for about 1 min. The PCR amplification protocol can further comprise the following conditions and steps in the following order: about one cycle of about 45xc2x0 C. to about 65xc2x0 C. for about 10 min; and about one cycle of about 72xc2x0 C. for about 10 min.
Also provides is a kit for amplification of olfactory receptor sequences comprising primer pairs that can amplify olfactory receptor transmembrane domain regions II through VII, II through VI, III through VII, or III through VI, e.g., SEQ ID NO:1 and SEQ ID NO:2 to amplify TM II through VII.
The invention also provides a library of olfactory receptor ligand-binding regions consisting essentially of olfactory receptor transmembrane domain regions II through VII, II through VI, III through VII, or III through VI, including partial domains, or a combination of domain sequences. The library of the olfactory receptor ligand-binding regions can be generated by PCR using degenerate primer pairs.
Also provided is a library of chimeric nucleic acid sequences comprising the following domains in 5xe2x80x2 to 3xe2x80x2 order: a nucleic acid encoding an amino terminal plasma membrane translocation domain; a nucleic acid encoding a first transmembrane domain; and a nucleic acid encoding an olfactory receptor ligand-binding region, wherein the chimeric nucleic acid sequence encodes a 7-transmembrane polypeptide that can transverse a plasma membrane seven times. The amino terminal plasma membrane translocation domain comprises an amino acid sequence as set forth in SEQ ID NO:3 (and encoded by a subsequence of SEQ ID NO:6):
In alternative embodiments, the nucleic acid encoding the first transmembrane domain can be just a polynucleotide sequence encoding SEQ ID NO:3, or, SEQ ID NO:6 (including 45 nucleotides upstream of the initiation codon) or a subsequence thereof.
The first transmembrane receptor of the sequences of the library can be a 7-transmembrane receptor region I domain, or subsequence thereof, e.g., the sequence between the Eco R1 and Pst 1 sites of the M4-chimeric olfactory receptor of the invention (SEQ ID NO:4), as schematically represented in FIG. 1A; the full length sequence of the hybrid receptor has an amino acid sequence as set forth in SEQ ID NO:55, a nucleic acid that can encode this protein is SEQ ID NO:54, described below.
The olfactory receptor ligand-binding regions of the library can comprise olfactory receptor transmembrane domain regions II through VII, II through VI, III through VII, or III through VI, or a combination thereof. These olfactory receptor ligand-binding regions can be generated by amplification, e.g., PCR, using degenerate primer pairs. The library""s nucleic acid sequence encoding transmembrane domain regions II through VII can generated by PCR amplification of nucleic acid using a first primer comprising a sequence 5xe2x80x2-GGGGTCCGGAG(A/G)(C/G)(A/G)TA(A/G/T)AT(A/G/P)A(A/G/P)(AG/P)GG-3xe2x80x2 (SEQ ID NO:1) and a second primer comprising a sequence 5xe2x80x2-GGGGCTGCAGACACC(A/C/G/T)ATGTA(C/T)(C/T)T(A/C/G/T)TT(C/T)(C/T)T-3xe2x80x2 (SEQ ID NO:2). The library can be generated from PCR-amplified nucleic acid isolated as or derived from genomic DNA, mRNA or cDNA derived from olfactory neurons or olfactory epithelium.
Exemplary ligand-binding regions comprising transmembrane domains II through VII ca be an amino acid sequence encoded by a nucleic acid selected from the group consisting of SEQ ID NO:11, SEQ ID NO:13, SEQ ID NO:15, SEQ ID NO:17, SEQ ID NO:19, SEQ ID NO:21, SEQ ID NO:23, SEQ ID NO:25, SEQ ID NO:27, SEQ ID NO:29, SEQ ID NO:31, SEQ ID NO:33, SEQ ID NO:35, SEQ ID NO:37, SEQ ID NO:39, SEQ ID NO:41, SEQ ID NO:43, SEQ ID NO:45 and SEQ ID NO:47, or an amino acid sequence selected from the group consisting of SEQ ID NO:12, SEQ ID NO:14, SEQ ID NO:16, SEQ ID NO:18, SEQ ID NO:20, SEQ ID NO:22, SEQ ID NO:24, SEQ ID NO:26, SEQ ID NO:28, SEQ ID NO:30, SEQ ID NO:32, SEQ ID NO:34, SEQ ID NO:36, SEQ ID NO:38, SEQ ID NO:40, SEQ ID NO:42, SEQ ID NO:44, SEQ ID NO:46, SEQ ID NO:48.
To generate the nucleic acids of the library, PCR amplification can comprise the following conditions and steps in the following order: about one cycle at about 94xc2x0 C. for about 2 min; about 30 cycles of about 55xc2x0 C. for about 1 min, followed by about 72xc2x0 C. for about one min. followed by about 94xc2x0 C. for about 1 min; about one cycle of about 55xc2x0 C. for about 10 min; and about one cycle of about 72xc2x0 C. for about 10 min.
The library can further comprise a carboxy terminal 7-transmembrane receptor transmembrane region VII domain or subsequence thereof, e.g., the sequence between the Bsp E1 and Xba 1 sites of the M4-chimeric olfactory receptor of the invention (SEQ ID NO:5), as schematically represented in FIG. 1A; the full length sequence of the hybrid receptor has an amino acid sequence as set forth in SEQ ID NO:55, a nucleic acid that can encode this protein is SEQ ID NO:54.
The library of nucleic acid sequences can also comprise the following domains in 5xe2x80x2 to 3xe2x80x2 order: a nucleic acid encoding an amino terminal plasma membrane translocation domain comprising a sequence as set forth in SEQ ID NO:3, a nucleic acid encoding a transmembrane region I domain comprising a sequence as set forth in SEQ ID NO:4, a nucleic acid sequence generated by polymerase chain reaction (PCR) amplification of mRNA or cDNA derived from olfactory epithelium using a first primer comprising a sequence 5xe2x80x2-GGGGTCCGGAG(A/G)(C/G)T(A/G)A(A/G/T)AT(A/G/P)A(A/G/P)(A/G/P)GG-3xe2x80x2 (SEQ ID NO:1) and a second primer comprising a sequence 5xe2x80x2-GGGGCTGCAGACACC(A/C/G/T)ATGTA(C/T)C/T)T(A/C/G/T)TT(C/T)C/T)T-3xe2x80x2 (SEQ ID NO:2), and a nucleic acid encoding a 7-transmembrane receptor transmembrane region VII domain comprising a sequence as set forth in SEQ ID NO:6.
Also provided are expression vectors (e.g., plasmids, viruses) comprising a nucleic acid sequence derived from the libraries of nucleic acid sequences of the invention. Transformed or isolated infected cells comprising a nucleic acid sequence derived from a library of nucleic acid sequences of the invention or an expression vector of the invention are also provided. Transgenic non-human animals comprising a nucleic acid sequence derived from a library of nucleic acid of the invention or an expression vector of the invention are also provided. In the transgenic animal, the expression vector can be a mammalian expression vector that can be expressed in olfactory epithelium or olfactory neurons.
The invention also provides a library of recombinant polypeptides translated or derived from the library of nucleic acids of the invention. Also provided are polypeptides isolated or derived from the library of polypeptides of the invention.
Also provided are methods of determining whether a test compound specifically binds to a mammalian olfactory receptor comprising the following steps: expressing a nucleic acid derived from a nucleic acid library of the invention under conditions permissive for translation of the nucleic acid to a receptor polypeptide; contacting the translated polypeptide with the test compound; and determining whether the test compound specifically binds to the polypeptide.
Also provided are methods of determining whether a test compound specifically binds to a mammalian olfactory transmembrane receptor comprising the following steps: contacting a cell stably or transiently transfected with a nucleic acid derived from a nucleic acid library of the invention; culturing the cell under conditions permissive for translation of the nucleic acid to a receptor polypeptide with the test compound; and determining whether the test compound specifically binds to the receptor polypeptide. In this method, the receptor polypeptide can be expressed as a transmembrane receptor with a ligand-binding site on the cell""s plasma membrane outer surface. The specific binding of the test compound to the polypeptide can be determined by measuring a change in the physiologic activity of the cell, wherein a change in the cell""s activity measured in the presence of the test compound compared to the cell""s activity in the absence of the test compound provides a determination that the test compound specifically binds to the polypeptide. The measured cell activity can be a change in the calcium ion (Ca2+) or cAMP concentration in the cell, which can be measured by loading the cell with a calcium ion-sensitive fluorescent dye before contacting the cell with the test compound. In this method any cell can be used, e.g., a human cell or a Xenopus oocyte.
Also provided are methods of determining whether a test compound specifically binds to a mammalian olfactory transmembrane receptor polypeptide in vivo comprising the following steps: contacting a non-human animal stably or transiently infected with a nucleic acid derived from the library of the invention or an expression vector of the invention with the test compound; and determining whether the animal reacts to the test compound by specifically binding to the receptor polypeptide, wherein the specific binding of the test compound to the polypeptide is determined by measuring a change in a physiologic activity of the animal, wherein a change in a receptor-encoding vector-infected animal""s activity measured in the presence of the test compound compared to a bare vector-infected animal""s activity in the presence of the test compound provides a determination that the test compound specifically binds to the mammalian olfactory transmembrane receptor polypeptide. In this method, the measured physiologic activity can be measured by an electroolfactogram. The vector can be a recombinant virus, e.g., an adenovirus expression vector.
The invention also provides a method of determining whether a test compound is neurotoxic to an olfactory neuron expressing an olfactory transmembrane receptor polypeptide comprising the following steps: contacting an olfactory neuron cell stably or transiently infected with a nucleic acid derived from a library as set forth in claim 8 or claim 10 or an expression vector as set forth in claim 23 with the test compound; and measuring the physiologic activity of the cell, wherein a change in the cell""s activity measured in the presence of the test compound compared to the cell""s activity in the absence of the test compound provides a determination that the test compound is toxic. In this method toxicity can be indicated by abnormal calcium ion, cAMP or plasma membrane homeostasis.
Also provided are peptide domains for the efficient translocation of a newly translated protein to a plasma membrane comprising an amino acid sequence as set forth in SEQ ID NO:3 or an amino acid sequence having conservative amino acid residue substitutions based on SEQ ID NO:3. Translocation domains within the scope of the invention include amino acid sequences functionally equivalent to the exemplary translocation domain of the invention SEQ ID NO:3. The peptide translocation domain can be at least about 20 amino acids in length, at least about 30 amino acids in length or at least about 40 amino acids in length. The peptide translocation domain can have a sequence as set forth in SEQ ID NO:3, or, be encoded by a nucleic acid comprising a sequence as set forth in SEQ ID NO:6. The newly translated protein can be a transmembrane protein, e.g., a 7-transmembrane protein receptor, e.g., an olfactory receptor.
The invention also provides a hybrid (chimeric) polypeptide comprising an amino terminal amino acid sequence comprising a peptide translocation domain of the invention and a second polypeptide sequence, wherein the second polypeptide sequence is not a rhodopsin polypeptide sequence. The second polypeptide sequence can be a transmembrane protein, e.g., a 7-transmembrane protein receptor, e.g., an olfactory receptor. Also provides are isolated or recombinant nucleic acid sequences encoding these hybrid polypeptides. For example, an exemplary chimeric polypeptide of the invention and a polynucleotide that encodes this hybrid, described in the Example below and schematically represented in FIG. 1A as the insert from BamH1 to XbaI, have the amino acid (SEQ ID NO:55) and nucleic acid (SEQ ID NO:54) sequence, respectively (restriction enzyme sites are also indicated):
A further understanding of the nature and advantages of the present invention is realized by reference to the remaining portions of the specification, the figures and claims.
All publications, GenBank deposited sequences, ATCC deposits, patents and patent applications cited herein are hereby expressly incorporated by reference for all purposes.